A typical conventional pipe joint of a pump produced from steel plate has a structure such as that shown in FIG. 1. At the discharge side, a pipe connecting flange 2 having a discharge opening 2a is welded to a discharge opening portion provided in the peripheral surface portion 1a of a casing body 1, and a thick-walled iron plate 3 is welded to the reverse side of the flange face of the pipe connecting flange 2.
At the suction side, on the other hand, a suction flange 4 having a suction opening 4a is welded to a suction opening portion provided in the suction-side side surface portion 1b of the casing body 1, and a thick-walled steel plate 5 having a bolt hole 5a is welded to the reverse side of the suction flange 4. It should be noted that in the figure, the reference numeral 6 denotes a suction partition plate, 7 a volute inner wall having bores 7a in the periphery thereof, 8 a casing cover, and 9 an impeller.
In the prior art shown in FIG. 2, a box shaped support member 15 is provided at the suction joint of a pump casing 11 formed from a thin plate (steel plate) in such a manner that the box shaped support member 15 surrounds a short suction pipe 12, the box shaped support member 15 comprising a suction-side casing wall 11a, a connecting flange 13 and a support member 14 which extends between the connecting flange 13 and the pump casing 11. In the figure, the reference numeral 16 denotes a casing end wall (see West Germany Patent Laid-Open Publication No. 3517828).
In the above-described prior art, the one (FIG. 1) in which a thick-walled steel plate is welded to the reverse side of the flange face of the pipe connecting flange has a disadvantageously high cost, although the flange face portion has a satisfactorily high strength. In the prior art (FIG. 2) in which the suction-side connecting flange 13 is supported by the support member 14 that is disposed outside the short suction pipe 12, since the whole of the connecting flange 13 having a thick wall, needs to be formed using a corrosion-resistant material and further, since the intermediary water passage (short suction pipe) 12 is also a separate member, the prior art necessitates the expenditure of a great many of man-hours and the cost is high.
In view of the above-described circumstances, it is an object of the present invention to provide a pipe joint for a pump which has a corrosion-resistant flow path and high rigidity at the flange joint surface and which is capable of preventing deformation by the application of an external force to the flange.